Southern took everything No. 1 Arundel threw at it Friday, intercepting four passes on its way to a 30-19 victory and one of the biggest upsets of the season.
Andrew Harris had two interceptions for the Bulldogs, returning one for a touchdown late in the fourth quarter to seal the win over the Wildcats (9-1).
Arundel had averaged more than 40 points entering the contest.
Davonte Burke rushed for 168 yards and scored touchdowns from 77 and 30 yards, part of a Bulldogs running game that gained 348 yards and dashed for three touchdowns against a Wildcats defense that had held opponents to less than 14 points per game.
Tyler Washington brought the Wildcats within one point in the second quarter on his 17th touchdown catch of the season, and Joseph Blackwell's 4-yard touchdown run put them ahead 19-14 in the third quarter.
Burke scored his second touchdown in the fourth quarter to give the Bulldogs the lead again, and Harris' interception return put the game away.
Annapolis Area Christian School 44, Friends School 0: The Eagles completed their first perfect season with a win over the visiting Friends at Meade.
James Anderson rushed for 114 yards and two touchdowns for the AACS (10-0), and Jon Hunter added 73 yards and two touchdowns. Hunter also returned a punt for a touchdown in the second quarter.
Tony Paige added a touchdown on a 38-yard interception return for the Eagles.
No. 6 River Hill 51, Mount Hebron 0: Jordan Griffin scored five touchdowns as the Hawks (9-1) routed the host Vikings.
Griffin rushed for three touchdowns, caught a 20-yard scoring pass and returned a fumble 14 yards for a touchdown.
River Hill has won its eighth straight Howard County championship.
No. 8 Archbishop Spalding 57, St. John's 36: K.K. Smith scored five touchdowns and the Cavaliers (8-3) beat the host Vikings.
Smith had 254 yards on 23 carries, helping Archbishop Spalding to 461 rushing yards and 527 total yards in the game.
D.J. Smith added 110 yards and two touchdowns, and J.D. Izon ran for 82 yards and a touchdown for the Cavaliers.
Zach Waller led the Cavaliers' defense with eight tackles, a sack and a fumble recovery.
No. 10 Hereford 49, Perry Hall 14: Fullback Vince DePaola had 30 carries for 202 yards and four touchdowns in as the host Bulls (9-1) topped the Gators.
Halfback Tim Bristol ran for 177 yards and two touchdowns as the Hereford offense recorded 430 rushing yards and seven touchdowns on 57 rushes.
No. 11 Boys' Latin 28, St. Paul's 12: Brandon Barnes scored two touchdowns as the Lakers (7-2) defeated the visiting Crusaders (6-3).
Barnes scored on an 8-yard run in the first quarter and threw a touchdown pass in the fourth.
Chris Rubino expanded on an eight-point halftime lead for the Lakers when he scored on a 96-yard kickoff return to start the third quarter.
Taylor Stothoff had two interceptions and a forced fumble and converted all four point-after attempts for Boys' Latin. Aaron Mack made eight tackles and had three sacks.
Boys' Latin joins Archbishop Curley and Archbishop Spalding for a tie in first place in the Maryland Interscholastic Athletic Association B Conference. A coin toss will decide who receives a bye in the first round of the conference tournament.
No. 12 Atholton 27, Wilde Lake 15: Brian McMahon and Andrew King scored two touchdowns each for the Raiders (8-2) against the visiting Wildecats.
Curtis Pumphrey and Brian Anthony accounted for 25 tackles for Atholton.
The Raiders will host the Wildecats next weekend in the first round of the 3A East playoffs.